1. Field of Invention
The present invention relates to a system for measuring a concentration of biomolecules and a method of measuring a concentration of biomolecules using the same. More particularly, the present invention relates to an ultra-sensitive magnetoreduction measurement system and an ultra-sensitive, wash-free assay using the same.
2. Description of Related Art
To measure the concentration of biomolecules in a specimen, such as serum or urine, immunoassay, which is based on the reaction of an antibody or antibodies to its antigen, is often applied. One such immunoassay is the enzyme-linked immunosorbent assay (ELISA). The conventional ELISA (or the so-called sandwich ELISA) requires one antibody (captured antibody) being bound to a solid phase attached to the bottom of a plate well. The sample with the unknown amount of antigen is then added and allowed to complex with the bound antibody. After the antigen is immobilized, another antibody (detection antibody) with the same antigen specificity as the immobilized captured antibody is added to form a complex with the antigen. The detection antibody can then be covalently linked to an enzyme. Between each step, the plate is typically washed to remove any unbound proteins or antibodies. After the final wash step, the plate is developed by adding a chromogenic substrate or fluorogenic substrate to produce a signal that indicates the quantity of biomolecules in the sample. In essence, the sandwich ELISA requires two kinds of antibodies (captured antibodies and detection antibodies). Further, the two kinds of antibodies bind to epitopes that do not overlap on the antigen. Basically sandwich ELISA is inapplicable for detecting molecules having a single active epitope, for example, small molecules. Other methodologies, such as competitive ELISA, LC/MS/MS (Liquid Chromatography/Mass Spectrometry/Mass Spectrometry), high-performance liquid chromatograph, capillary electrophoresis, have also been applied to assay single-active-epitope biomolecules. However, these methods are normally non-direct, costly or involve complicated sample preparation or assay processes.
In recent years, alternative approaches have been explored to quantitatively detect biomolecules. For example, bio-functionalized magnetic nanoparticles, in which the surfaces of magnetic nanoparticles are coated with bio-receptors, have been used to mark specific biomolecules. Then, the differences in the magnetic properties of the biomolecules marked by or conjugated with the bio-functionalized magnetic nanoparticles are measured for determining the amounts of the biomolecules. These assays using bio-functionalized magnetic nanoparticles as markers are referred to as magnetically labeled diagnosis (MLD).
Several groups of researchers have reported high potential methodologies for MLD, for example, the measurements of magnetic relaxation, magnetic remenance, mixed-frequency magnetic susceptibility, saturated magnetization, etc. According to the results from these methodologies of MLD, some have demonstrated the merit of high convenience, while others exhibit the advantage of high sensitivity.